The present invention relates to a process for the production of superconducting conductors of the type comprising a plurality of filaments of an alloy containing niobium and titanium as base materials, and a composite matrix of copper, aluminium or alloys of these elements in which the filaments are disposed, and which serves to stabilise the superconductor.
As is known, superconducting conductors are normally constituted by a plurality of filaments of a niobium/titanium alloy embedded in a matrix, normally of copper, which has substantially the form of an integral continuous solid of constant cross-section in which the said filaments are embedded, and which serves both a mechanical function and, above all, the function of stabilizing the superconductor, that is to say of the providing an alternative path for the current when the superconductor section passes to the normal state. The said matrix, instead of being copper, can be made of another material such as aluminium or an alloy of aluminium or copper.
These conductors are normally utilized for applications in which there are magnetic fields. For particular applications a particularly strong stabilisation is required, which can only be obtained with a high ratio between the volume of the material of the matrix to the volume of the material of the filaments, which ratio can in some cases be greater than 10. In these conditions, instead of fabricating a superconducting conductor having a single matrix with a very high volume with respect to that of the filaments disposed in it, it is more convenient from the economical point of view, and more reliable from a technical point of view, to provide a composite matrix obtained by coupling a superconductor conductor having a relatively low value of the above defined ratio, for example lying between 1 and 2, with a blank or casing of copper (or aluminium or other alloy) in which the superconducting conductor is inserted. To make a superconducting conductor having a composite matrix obtained in this way a process is used which substantially comprises the following phases.
In a blank having a suitable cross-section, which is normally rectangular, there is formed a longitudinal groove with a substantially U-shape form and subsequently, into this groove, there is inserted a superconducting conductor having a rectangular section, and this latter is connected both mechanically and electrically to the blank itself by means of a layer of brazing material disposed between the outer surface of the conductor and the inner surface of said groove. The superconducting conductor obtained with this process has various disadvantages.
Above all, the electrical and heat exchange between the inner superconducting conductor within the blank and this blank itself takes place only on 3 of the 4 faces of the conductor. Moreover, the electrical axis of the superconducting conductor thus obtained (which coincides with the geometric axis of the filaments disposed in it) does not coincide with the geometric axis of the conductor itself. Moreover, the process described can only be used with superconducting conductors having rectangular sections since with those having circular sections it is not possible to effect the above described connection between the conductor and the blank. Moreover, the described process comprises numerous phases, some of which are intended to the preparation of the blank into which the initial superconducting conductor must be inserted. Finally, this process is difficult to perform when the section of the superconducting conductor is very small, a condition which occurs when the maximum transverse dimension thereof is less than 4 or 5 mm.